Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – Objective type
Reexamination Certificate
2000-08-28
2001-06-26
Manuel, George (Department: 3737)
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
Objective type
Reexamination Certificate
active
06250761
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to retinoscopes and more particularly to spot retinoscopes or dual mode retinoscopes which can function either as spot retinoscopes or streak retinoscopes.
BACKGROUND TO THE INVENTION
Retinoscopes are used to obtain objective indications of any refractive errors in eyes. To that end a retinoscope projects a small patch of light onto the fundus of an eye under examination. The user of the retinoscope (i.e. the person conducting the examination) then moves the device so as to move the emitted beam in a given direction, and views the direction in which the patch appears to move after having been refracted and reflected by the eye under examination. The direction of the apparent movement of the patch, relative to the actual movement of the retinoscope, enables the user to determine whether the eye under examination is long-sighted or short-sighted. The user can then quantify the refractive error of the eye under examination by interposing correction lenses of various strengths between the eye under examination and the retinoscope until the user finds a correction lens for which movement of the retinoscope causes substantially no apparent movement of the patch of light. This is referred to the “neutral point” of the eye under examination, and the power of the correction lens that achieves this is indicative of the refractive error.
A conventional spot retinoscope has a light source, such as a light bulb with a conventional helical filament, light from which passes through a focusing lens system, and is then reflected by an angled, semi-silvered or apertured mirror into the eye under examination. An annular stop is interposed between the lens system and the light source, and the shadow cast by the stop defines the boundary of the substantially circular patch of light projected into the eye under examination. The image of the patch of light projected into the eye is viewed by the user from the opposite side of the mirror.
Known spot retinoscopes also have a facility for moving the lens system so as to alter the divergence of the beam of light being directed into the eye under examination, so as to enable the user to alter the size of the projected spot. Large refractive errors cause slow movements of the reflex which are difficult to detect if the spot is large. By reducing the spot size, the movement is made easier to detect. Small refractive errors cause fast movements and are more easily detected when the spot is large.
However, even with a large spot, it can be difficult to determine whether the neutral point has in fact been reached, or whether there is a small amount of movement of the projected spot. Thus, errors in the determination of refractive error can occur if the user of the retinoscope believes the neutral point has been reached, whereas in fact movement of the retinoscope does cause a small undetected amount of movement of the projected spot.
SUMMARY OF THE INVENTION
According to the invention, there is provided a spot retinoscope for use in assessing the of refractive error of an eye, the retinoscope having viewing means for viewing the eye under examination, receiving means for receiving a source of light, projection means for directing a beam of light into an eye under examination thereby to project a spot of light into said eye, and focusing means for altering the divergence and convergence of said beam, the focusing means being movable from a normal position in which the beam is divergent, or converges to a point, in use, behind the eye under examination, to a cross-checking position, in which the beam is convergent on a point which, in use, is sufficiently far in front of the eye under examination to enable the user to detect movement of the patch of light projected onto the retina under examination where any refractive error in said eye has not been corrected by a lens placed between the eye and the retinoscope.
Even if movement of the retinoscope causes only a very small amount of perceived movement of the projected spot in the eye under examination when the focusing means is in its normal position, it has been found that the same movement of the retinoscope will produce movement of the projected spot in the opposite direction when the focusing means is in its cross-check position. Thus, when the user has found what is believed to be the “neutral point” for a patient, using the focusing means is in its normal position, the user can check to determine whether the neutral point has in fact been reached by moving the focusing means into its cross-check position. If the neutral point has been reached, movement of the retinoscope will still not cause perceived movement of the projected spot, whereas there will be a detectable movement of the spot if the neutral point has not been reached.
Thus, the invention enables the user to confirm that the neutral point has been reached.
In the past, a similar type of cross-checking has been performed using certain design of streak retinoscopes. However, as far as the Applicants are aware, those streak retinoscopes were not specifically designed to have a cross-checking feature, and the focusing systems of known spot retinoscopes do not have a position corresponding to the cross-check position of the focusing means of the present invention.
Preferably, when in its cross-check position, the focusing means is so arranged that, in use, it causes the beam of light emitted by the retinoscope to converge on a point not more than approximately 300 mm from the retinoscope.
It has been found that, with a retinoscope at normal viewing distances from the eye, any movement of the projected spot when the focusing means is in its cross-check position is greatly reduced if the point of convergence is any closer to the eye than 300 mm.
It will be appreciated that the invention is not restricted to retinoscopes which are supplied with their own light sources, since the light source for a retinoscope would normally be replaceable. Thus, the invention includes within its scope a retinoscope which does not have an integral light source, but is intended for use with a separately supplied source.
Conveniently, however, the retinoscope does include a light source for emitting the light for said beam.
Preferably, the light source is interchangeable with a further light source, the further light source being arranged to emit light over an elongated substantially linear area to cause the retinoscope to project a streak of light into the eye under examination, the retinoscope including rotation means for rotating the streak to enable to retinoscope to be used as a streak retinoscope.
Preferably, the further light source has a linear light-emitting element, for example a filament, the projected image of which constitutes said streak.
The retinoscope may to advantage include a stop, preferably an annular stop, situated in the path of light from the light source and arranged to cast a shadow that bounds the beam of light projected from the retinoscope so as to cause a spot of light to be projected into the eye under examination, the light source being such as to provide substantially uniform illumination of the spot.
To that end, the light source may, for example, comprise a bulb having a helical filament.
Where the retinoscope can be used as a spot or as a streak retinoscope, the range of movement of the focusing means is preferably such as to enable an image of either the inner periphery of the stop or, where the further light source is used, the linear element to be projected into the eye under examination.
To that end, the focusing means may to advantage comprise lens means which is slidably mounted in the retinoscope and is movable towards or away from the stop and light source over a distance of at least 14 mm.
It has been found, with this range of movement, the lens means can not only enable the retinoscope to be used as a spot retinoscope or streak retinoscope (depending on the nature of the light source used), but can also allow the retinoscope to be used to provide the above described cross-check in
Church Kelvyn
Little Mervyn Aubrey
Keeler Limited
Lee Mann Smith McWilliams Sweeney & Ohlson
Manuel George
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